Agreements - Jazz Pharmaceuticals (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Aug. 31, 2017 USD ($) product item	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Agreements disclosures
Remaining arrangement consideration to be recognized as license revenue		$ 81,522	$ 93,752
Jazz Pharmaceuticals
Collaborative Agreements disclosures
Number of early stage ADC programs | item	2
Number of ADC programs | item	3
Payments received under collaboration agreement	$ 75,000
Potential milestone payments	$ 100,000
Term of agreement	7 years
Number of products with rights to co-commercialize | product	1
Number of products with rights under certain limited circumstances | product	2
Offset to research and development expense		2,000
Number of development and commercialization licenses | item	3
Remaining arrangement consideration to be recognized as license revenue	$ 75,000	$ 75,000